The general concept of gasification of organic input material is relatively well known, including pyrolysis gasification in which organic input material undergoes a chemical and physical change to charcoal in the absence of a flame, producing in the process fuel gas such as carbon monoxide and hydrogen, in addition to other volatiles. A disadvantage to many gasification systems, including those incorporating a pyrolysis reduction process, is that tars and other undesirable volatiles are produced during the process. These volatiles are present in the synthesis gas and make the gas undesirable, as well as fouling the equipment for producing the gas.
Some information is known relative to controlling tars and pyrolysis volatiles, including, among others, controlling the particular configuration of the gas reduction bed, the temperatures of the various layers in the reduction bed, and the character and arrangement, including size, of the input material. Illustrative of this body of knowledge is U.S. Pat. No. 4,530,702, in the name of Fetters, et al, titled Method for Producing Fuel Gas From Organic Material, Capable of Self-Sustaining Operation.
However, there are still presently many unknowns concerning the reliable production of essentially tar-free fuel gas. For instance, it is not completely understood what are the significant process control features and/or characteristics of the gas production bed which tend to prevent creation of tars and other volatiles and to maintain efficient operation of the gasifier.
In addition, a typical by-product of the gasification process is the production of charcoal. This charcoal typically must be periodically removed from the gasifier and disposed of, in some fashion. Unfortunately, the market for charcoal produced by conventional gasification systems is uncertain and disposal problems thus sometimes exist. This increases the overall expense of the gasification system, due to a lack of adequate return on the charcoal produced.